The present invention pertains to an improved anti-marking sheet and method for providing improved support along the entire width of a freshly printed sheet material in a printing press or similar machine and particularly to an improved anti-marking sheet/jacket for a print press transfer/perfector cylinder.
Since the first printing press was placed into operation, operators have wrestled with the problem of freshly printed sheets becoming undesirably marked as they travel from one printing station to the next. To solve this problem, press manufacturers and innovators have tried various methods ranging from tracking/skeleton wheels, pneumatic devices, to cylindrical coverings of sandpaper, glass beaded paper, dimpled metal and loose mesh fabric. While most of these devices are effective to some degree, none of them fully satisfy the needs of a printer. A brief history illustrating the development of such anti-marking systems is outlined below.
In U.S. Pat. No. 2,085,845, Binkley applies xe2x80x9ca coating granular material such as silicon carbide, emery, etc.xe2x80x9d onto the face of the fabric which has a barrier coating adhered onto rear side and is adhered to the make-ready and then clamped to the tympan roll. Here, Binkley asserts that using a sandpaper-like material will provide the advantage of decreasing the marking of freshly printed sheets. In U.S. Pat. No. 2,555,319, Cross also studies the application of granular materials to rolls within a printing machine and tests granular materials ranging from glass culets, silicon carbide and aluminum oxide and compares them to spherical glass beads. He asserts that the spherical glass beads offer a smooth and round uniform surface that is superior to that of granular grit. Cross further asserts that spherical beads allow the freshly printed/inked sheet to be uniformly supported by the tops of millions of uniform glass beads resulting in a decrease of marking printed sheets. Cross also teaches of both the benefits of back coating a porous substrate and over-coating the beaded side to improve adhesion of the glass beads to the substrate as well as to aid in repelling printing inks/solvents.
In U.S. Pat. No. 4,694,750, Greene attempts to improve on known rolls having granular surfaces by using xe2x80x9can elastic member that is attachable to each flange and is stretchably positionable around the circumferential granular surface.xe2x80x9d Greene""s use of elastic bands to make an easily installable anti-marking product falls short in two areas: first the elastic bands impede use of the full width of the cylinder (thus limit sheet size). Second, since the elastic bands run circumferentially around the cylinder, they do not provide adequate uniform tension across the entire sheet resulting in movement of the granular sheet and ultimately marking results.
In U.S. Pat. No. 4,688,784, Wirz employs perforations in various textured surfaced anti-marking sheets that come into alignment with a hole or bore of the air ducts in the cylinder. The purpose of using compressed air is to aide in the transport of the freshly printed sheet as it travels mark-free from one printing station to the next.
In U.S. Pat. No. 3,791,641, DeMoore uses an ink repellent PTFE sheet that is affixed to skeleton wheel. Later, in U.S. Pat. No. 4,402,267, DeMoore improves upon this design by adding xe2x80x9ca loosely retained ink repellent fabric coveringxe2x80x9d known in the industry as SUPER BLUE(trademark) over the cylinder sheet. In U.S. Pat. No. 5,842,412, Greenway et al. also uses a light weight fabric with preferred axial air permeability not less than about 0.138 cfm and a surface structure with closely spaced features of a spacing not more than about 0.125 inch.xe2x80x9d This fabric is known in the industry as QUACK(trademark).
In U.S. Pat. No. 6,203,914 B1, Sudo et al. follows Cross""s process for manufacturing an ink repellent anti-marking sheet as disclosed in U.S. Pat. No. 2,555,319. Sudo uses a urethane crosslinked silicone top coat well known in the industry and disclosed in U.S. Pat. No. 5,415,935 as an ink-repellent coating over the glass beaded surface.
In U.S. Pat. No. 6,244,178 B1, DeMoore recognizes the importance of easy installibility and further improves his SUPER BLUE(trademark) fabric to include asserted improvements such as pre-stretched, pressed flat and pre-cut to the cylinder dimensions complete with anti static/conductive filaments and ink-repellent coating.
Despite the efforts made in these many patents or products in the market today, marking of printed sheets in printing presses remains problematic.
It is therefore an object of the present invention to overcome the problems of printing press anti-marking systems in the prior art, and particularly to solve the problem of wet ink marking/smearing on the sheet/web due to the contact of freshly printed sheets with the transfer cylinder or the anti-marking surface covering it. The present invention recognizes that for an anti-marking system to be optimal, it preferably meets four conditions:
1. Technically, the surface of the anti-marking system should perform its function of uniformly supporting and conveying the freshly printed sheet from one printing station to the next without marking the freshly printed sheet.
2. Installability, the anti-marking sheet/jacket should be uniformly applied to the surface of the desired cylinder. If the operator cannot easily apply the anti-marking cover uniformly over the cylinder, then ridges, bubbles and creases develop which by themselves create undesirable marks.
3. Durability, the anti-marking product should withstand contact with hundreds of thousands of printed sheets to include various thickness"" and the inadvertent creased/folded sheet which typically can damage an anti-marking system.
4. Cleanability, the anti-marking surface needs to be easily cleaned upon completion of the printing job to include ink and oil residue from the printing machine.
The present invention provides an improved method and apparatus for supporting and conveying sheet or web material that has been freshly printed on at least one side wherein the printed material is supported by a cylindrical roll or skeleton or tracking wheels which has mounted on the outer surface thereof an anti-marking material having at least two layers. The anti-marking material comprises at least an outer textured surface layer and an inner microcellular layer. The outer textured surface layer is the surface that actually comes in contact with the wet printed sheet.
The contact between the outer textured surface and the wet printed ink is important to anti-marking performance. Too much surface or uneven contact will cause the wet ink to smear or mark. Too little surface or uneven contact will cause the sheet to be inadequately supported (resulting again in marking) as it is transferred from one printing station to the next. The pattern of the textured surface is therefore preferably uniform across the entire surface and strikes a delicate balance between adequate support for and good release of the wet printed sheet without marking.
A textured surface that contains uniform raised contact points spaced apart by lower areas is preferred. For embossed patterns, the percent area of the raised ridges should preferably not exceed about 60% or the contact area with the wet printed sheet will not release cleanly without marking. The percent area of the raised contact can be minimized by careful tooling of the embossing roll. Care should be taken to uniformly space the raised contact points while minimizing their surface area. The minimum area in this scenario approaches zero and is constrained only by current manufacturing processes to single digit percentages.
In accordance with another aspect of the present invention there is provided a method and apparatus for supporting and conveying sheet or web material that has been freshly printed on at least one side wherein the printed material is supported by a cylindrical roll or skeleton/tracking wheels which has mounted on the outer surface thereof an anti-marking material comprising an outer glass bead textured surface layer and an inner microcellular layer. In this embodiment, the textured surface is created by adhering glass/zirconia/plastic beads uniformly to the outer surface. Here, only the convex portions of the glass beads come in contact with the wet printed sheet. Glass beads are extremely durable and provide an excellent uniform surface to support the sheet while allowing for any excess ink to slide down the glass bead and collect in the low areas between the bead peaks.
The inner microcellular layer is the perfect compliment to the textured surface. When adhered to the planar or flat underside of the textured surface, the microcellular layer conforms to the outer surface of the cylinder ensuring a perfectly uniform outer textured surface. The key features of the microcellular layer are that it is both compressible and resilient. In one embodiment, a five pound/cubic foot polyolefin microcellular foam was extruded and laminated to the planar surface. In another embodiment, a thirty pound/cubic foot urethane microcellular foam was extruded and laminated to the planar surface. In yet another embodiment, a rubber saturated paper was laminated to the planar surface. In all these cases, the microcellular layer provided the required compression under weight/pressure and were sufficiently resilient when the weight/pressure was removed.
In accordance with one embodiment of the present invention, the build up of ink is prevented on the textured surface through the use of an ink-repellent coating applied thereon. In one embodiment, the ink-repellent coating is a cross-linkable silicone or fluorocarbon.
In accordance with another embodiment of the present invention the buildup of static or electrical charge on the textured surface is prevented through the use of either conductive coatings or an anti-static coatings applied thereon to one or both sides of the anti-marking sheet. Conductive coatings can be metal foils or metallized substrates. Anti-static coatings are preferably salt based. In order to effectively dissipate static electrical charges, it is critical to ground the surface of the anti-marking material to the cylinder or some other suitable ground.
In accordance with another aspect of the present invention, a method is provided for easily and quickly affixing an anti-marking jacket to a transfer cylinder. The process begins by precutting an anti-marking sheet of the present invention to the proper sheet dimensions for a given cylinder. Depending on the press model, cylinder location and the personal preferences of the press operator, the sheet may be either mechanically attached or adhesively adhered to the cylinder. In one embodiment, a magnetic strip was adhesively adhered to the longitudinal edges of the anti-marking sheet and magnetically attached to the cylinder.
In another embodiment, a Velcro(trademark) or other hook and loop type fastening strip can be adhered to the longitudinal edges of the anti-marking sheet and mechanically affixed to a cylinder having a mating portion of Velcro(trademark) affixed along its longitudinal edges. Alternatively, a fibrous Velcro(trademark) backing can be adhesively adhered to the base of the anti-marking sheet and be mechanically affixed to the tracking/skeleton wheels having a mating portion of Velcro(trademark) affixed along the edge of its circumference.
In a still further embodiment, a double-sided pressure sensitive tape can be adhered to the longitudinal edges of the anti-marking sheet and mechanically affixed to the cylinder. Alternatively, double-sided pressure sensitive adhesive can be adhered to the entire sheet of the present invention and then applied to the cylinder. In a further alternative, a double-sided adhesive tape can be adhered along the circumference edge of a tracking/skeleton wheel and then the anti-marking sheet can be applied to the wheel in such a manner as to form the shape of a cylinder.
In accordance with another embodiment of the present invention, a method for easily and quickly affixing an anti-marking jacket to the transfer cylinder is provided using at least one elastic loop affixed to the longitudinal edge of an anti-marking sheet of the invention. In accordance with another embodiment of the present invention, this elastic loop jacket is specifically designed to fit on a Heidelberg printing press.
In accordance with another embodiment of the present invention, a method for easily and quickly affixing an anti-marking jacket to the transfer cylinder of a Heidelberg Speedmaster 74 printing press is provided using reusable affixing hardware (for example, eight clips supported onto a stainless steel rod that slides into a sewn loop of an anti-marking sheet of the present invention) on one longitudinal edge of the present invention and a flat permanently affixed strip (stainless steel or other suitable firm strip) to the other. The operator first slides the flat end into a groove and firmly clamps it down in place. Holding the clip end of the jacket, the operator slowly rotates the cylinder until the clips come in alignment with and fit over eight pins on a support bar.
The pressman next tightens a center bolt that tensions the jacket over the transfer cylinder. This jacket may be installed in five minutes. When the jacket materials useful life is over, the stainless steel rod and eight clips are saved and re-used on a new jacket saving hardware costs. Alternatively, an anti-marking sheet of the present invention may be laminated to a thin conductive sheet metal. The ends of this sheet metal may be easily die cut and bent to affix both over these eight pins as well as in the thin groove. The jacket is tensioned up in a similar manner.
In another embodiment of the present invention, holes are perforated through the anti-marking sheet of any of the above constructions allowing for pressurized air to flow through specific air feed holes bored through the transfer cylinder. Air is blown through these feed holes facilitating the mark free transport of the freshly printed sheet as it moves from one print station to the next. The microcellular layer is of particular benefit in these perforated sheets as the compressible layer forms an air tight seal between each perforated hole and the transfer cylinder""s surface thus ensuring pressurized air is fully directly through each hole and does not escape laterally. The result is a uniform air pressure through each hole surrounding the entire cylinder. Constant pressure through uniform air feed holes ensures constant air volume and velocity providing for a mark free transport of the wet printed sheet.
In another embodiment of the present invention, the anti-marking sheet of the invention having at least two layers could be alternatively used for multiple other cylinder coverings besides transfer cylinders. In one embodiment the two plus layer sheet was mounted on a plate cylinder with the plate mounted thereon. In another embodiment, the two plus layer sheet was mounted on both the blanket and impression cylinders. In both the plate and impression cylinders, the outer textured layer coupled with the inner microcellular layer proved a suitable combination for improving the quality of print on the sheet. To meet the economical constraints of packing sheets, the textured surface may be omitted.
In yet another embodiment of the present invention, the anti-marking material of the invention having at least two layers could be slit into narrow width rolls that could be easily applied to the cylinders of flexographic/web printing machines for mark free transitions. The rolls of anti-marking tape were used to spiral wind around the transport and nip cylinders in such a manner that during application, the inner microcellular layer compressed and held tightly to the surface of the cylinder while the outer textured layer lay perfectly flat around the circumference of the cylinder.